A light-emitting device includes a P-N junction diode having a characteristic of converting electrical energy into light energy. The light-emitting device may include compound semiconductors belonging to group III and V on the periodic table. The light-emitting device can represent various colors by adjusting the compositional ratio of the compound semiconductors.
When forward voltage is applied to the light-emitting device, electrons of an N layer are combined with holes of a P layer, so that energy corresponding to an energy gap between a conduction band and a valance band may be generated. The energy is mainly emitted in the form of heat or light. In the case of the light-emitting device, the energy is generated in the form of light.
For example, a nitride semiconductor represents superior thermal stability and wide bandgap energy so that the nitride semiconductor has been spotlighted in the field of optical devices and high-power electronic devices. In particular, blue, green, and ultraviolet (UV) light-emitting devices employing the nitride semiconductor have already been commercialized and extensively used.
Recently, as the demand for a high-efficiency light-emitting device is increased, the enhancement of light intensity has been issued.
In order to enhance the light intensity, various attempts have been carried out to improve the structure of an active layer (MQW), an electron blocking layer (EBL), and a lower layer of the active layer, and good results are not obtained.